[#426] cmd/neofs-node: Add metrics collector in node

Disabled by default.

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

cmd/neofs-node/metrics.go

@@ -0,0 +1,15 @@
+package main
+
+import (
+	"github.com/nspcc-dev/neofs-node/pkg/util/profiler"
+)
+
+func initMetrics(c *cfg) {
+	c.metrics = profiler.NewMetrics(c.log, c.viper)
+}
+
+func serveMetrics(c *cfg) {
+	if c.metrics != nil {
+		c.metrics.Start(c.ctx)
+	}
+}